ON PNEUMATICS

...will stop for the same aforementioned reason; but if we make the hole at E., this water will flow out until the water in the vessel has dropped so far that its surface is level with the mouth of the pipe C. And if we wish to draw all the water out of the vessel, we shall lower the mouth C. to the very bottom of the vessel, though as far from it as we think will suffice for the water to flow. Some say the reason why the pierced and bent pipeoriginal: "canna"; used here to describe the siphon tube produces this effect is because the quantity of water in the longer legoriginal: "gamba"; referring to the vertical sections of the siphon has the power to attract, and in effect pulls, the smaller [leg]. But how false this cause is, and in what error whoever believes this remains, may be seen from this: Let a pipe be made such that the interior leg is long and thin, and the exterior leg much shorter but wider, so that it holds a greater quantity of water than the long leg. If it were filled with water, and the longer leg then placed in a vessel of water or a well—which would be the same as if we made the exterior leg flow—since it has in itself a greater abundance of water than the interior one, it would also have the power to attract the water from the larger [leg], and with it would also pull that which is in the well. When it began to flow, it would draw it all out or flow forever, because the quantity of the exterior water is greater than that in the interior leg. But since the truth of where this derives from does not appear, we do not approve of the aforementioned reason.

Instead, let us look at the natural cause of this, saying that every continuous fluidoriginal: "humido continuo"; a Renaissance term for any liquid that maintains a physical connection without gaps and still liquid takes a spherical surface whose center is the same as the Earth’s. But if it is not standing still, it flows until it reduces itself to a spherical surface, as was said above. Let two vessels be taken by us, and in each of them let water be placed; let us also fill the pipe with water, and with our fingers let us plug its mouths, placing one end in one of the aforesaid vessels so that it is submerged in the water, and similarly let us place the other leg in the other vessel. All the water is thus made continuous, because the water in both vessels becomes joined with that in the pipe in such a way that it is all one continuous body. If, therefore, the said waters which were first in the vessels are at the same surface level, being made continuous by the bent pipe submerged in them, they will rest and remain still. But if one of them is lower than the other, because the water is made continuous, it is also necessary by this continuity that the higher one flows into the lower one, until either all the water in the aforesaid vessels is reduced to the same surface level, or until one of the said vessels is empty. But if they equalize at the same surface level, the waters in these vessels will stop, both one and the other, so that the water in the pipe will also remain still. Thus, given that one leg and the other are equally submerged in each of said surfaces (supposing they are equal), the water within it will stay still. If the pipe is suspended so that it declines neither here nor there, it is again necessary that the water stops, whether it has equal width or if one leg is much larger than the other; for in this, the reason why the water stands still or flows does not depend on that, but derives from whether its mouths in the water are level.

Now let us say: why (when the pipe is suspended) does the water not flow down by its own gravity In this context, "gravity" refers to the natural heaviness or weight of the liquid, it being lighter than the air beneath it? It is for no other reason, certainly, than because the place of the whole cannot be...